lim(x-->1) sin(x² - 1)/(x - 1)
= lim(x-->1) sin(x² - 1)/[(x² - 1)] * (x + 1)
= lim(x-->1) (x + 1)
= 2
因为那是x² - 1,当x趋向1时,x² - 1同样趋向0,还是可用等价无穷小
lim(x-->1) sin(x² - 1)/(x - 1)
= lim(x-->1) sin(x² - 1)/[(x² - 1)] * (x + 1)
= lim(x-->1) (x + 1)
= 2
因为那是x² - 1,当x趋向1时,x² - 1同样趋向0,还是可用等价无穷小